This invention relates generally to a method and apparatus for driving a non-impact type printer, and more particularly, to a method and apparatus for driving an ink on-demand type jet printer head providing a wide range of gradation in the printed indicia. Gradation printing with an on-demand type ink jet printer head has heretofore been accomplished by changing the voltage amplitude of a drive pulse or by changing the pulse width of the drive pulse applied to the ink jet head. With these earlier techniques, the ink droplet volume ratio is in a range of only 1.5 to 2. From this ratio the resultant print can be given only 3 to 5 gradations in the density of the printed indicia. Thus, the conventional methods are not yet practical. Ink stagnation in the nozzle is also a problem when printer usage is intermittent.
In an on-demand type ink jet printer head, the drive period can be changed in a range from several hundreds of microseconds to infinity. Therefore, in order to improve and stabilize the print quality with the various charactistics of the head maintained unchanged at each drive frequency, it is necessary to set the maximum operating drive frequency much lower than the maximum frequency with which the head can actually jet ink. In particular, after each drive pulse, transient pressure waves exist in the ink supply system which require considerable time to dampen such that the starting conditions for each drive pulse are the same. When the starting conditions in the ink supply system are not stabilized at the time of the next drive pulse, the printed dots vary in quality and the overall quality of the printed matter is deteriorated.
What is needed is an ink jet printer head which operates at high speed and yet provides uniform quality of printing and density gradations.